The present invention relates to an image signal generating apparatus, an image display unit, and a control method for an image display unit useful in, for example, a personal computer system having a plurality of image display units.
Examples of image display units to which the invention is applicable include liquid crystal display (LCD) units, cathode-ray tube (CRT) units, digital micromirror device (DMD) units, plasma display panel (PDP) units, and field-emission display (FED) units.
As a conventional example of a system with multiple image display units, FIG. 1 shows a system in which a single image signal generating unit 101 supplies separate image signals through separate cables to four image display units 102 simultaneously. The image signals are generated separately by four image signal generators 103. The image signal generators 103 comprise, for example, hardware circuits disposed on one or more expansion cards installed in a personal computer. Each image signal generator 103 has a separate cable connector. Each image signal, and each image display unit 102, has a standard resolution such as seven hundred sixty-eight lines with one thousand twenty-four picture elements or pixels per line (1024×768 pixels). The four image signals may be combined, as shown, to form a single image with a higher resolution (2048×1536 pixels).
A problem with this conventional system is that each time an image display unit is added to the system configuration, another image signal generator 103 and another interconnecting cable are required. The number of image display units 102 that can be controlled is thus limited by the expansion capacity of the personal computer. Often, the personal computer lacks space for an adequate number of display signal generators 103, or for an adequate number of cable connectors.
FIG. 2 shows another conventional example, in which the image signal generating unit 101 has a single image signal generator 103 that generates a high-resolution signal (for example, a signal with a resolution of 2048×1536 pixels). The high-resolution signal is distributed to four image display units 102, each having a lower resolution (1024×768 pixels, for example). Each image display unit 102 displays one quadrant of the image.
A problem in this configuration is that high-speed digital-to-analog (D/A) and analog-to-digital (A/D) converters are required to generate and process the high-resolution image signal. High-speed D/A and A/D converters are expensive, and their performance limits both the attainable resolution and the quality of the displayed image. In practice, the limited performance of available D/A and A/D converters tends to degrade the image quality.